Power line carrier communication apparatus

ABSTRACT

A power line carrier communication apparatus which prevents leakage of an electromagnetic wave and stably operates while employing a simplified configuration is provided. 
     The power line carrier communication apparatus may include a transmission circuit which is connected to a power line and which transmits a signal to the power line; a reception circuit which is connected to the power line and which receives the signal from the power line; and an output suppression circuit which is connected to the power line and which, by connecting a signal attenuating element between the transmission circuit and a common only when the transmission circuit transmits the signal, suppresses an output of the signal transmitted from the transmission circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power line carrier communicationapparatus.

2. Description of the Related Art

Conventionally, power line carrier communication which uses a power lineas a communication line is performed. A power line carrier communicationapparatus is an apparatus which performs such communication using apower line, and can perform data communication to each power linecarrier communication apparatus connected by the power line.

While there are various schemes of power line carrier communication,there are roughly carrier band transmission for modulating data to becommunicated using a carrier wave of several Hz to several tens of MHzas a carrier, and baseband transmission which does not use a carrierwave. The carrier baseband transmission can not only performcommunication which is hardly influenced by noise in the surrounding byselecting a frequency of a carrier wave but also further preventcommunication from being influenced by noise by using a plurality ofcarrier waves in combination, and therefore is used for communication inmany apparatuses.

Japanese Patent No. 3931666 discloses a power line carrier communicationapparatus which is configured to suppress the amount of powerconsumption as much as possible in a carrier band transmission whichuses a plurality of carrier waves in combination.

SUMMARY OF THE INVENTION

However, it is necessary to process signals whose number corresponds tothe number of frequency bands of carrier waves to be used since aplurality of carrier waves is used for the above carrier bandtransmission, and therefore there is a problem that multiple elementsare required and thereby increase manufacturing cost. In addition,frequencies of carrier waves are set sufficiently high compared to a bitrate of data to be communicated, and therefore there is also a problemthat elements which operate at a high speed are required, and therebyincrease manufacturing cost.

On the other hand, when baseband transmission is performed, atransmission signal is superimposed on a power line which feeds power,and therefore since transmission efficiency of a signal is poor comparedto communication which uses a normal communication line and atransmission signal is likely to attenuate, it is necessary tosuperimpose a transmission signal of a higher level on the power line.However, what is not preferable is that, when a level of a signal to betransmitted is too high, this signal is likely to leak to a surroundingas an electromagnetic wave. Hence, although it is also possible tosuppress attenuation of a transmission wave by decreasing an outputimpedance of a signal, in this case, a problem that an input level of asignal received using the same power line weakens.

The present invention is made in light of the above matter, and anobject of the present invention is to provide a power line carriercommunication apparatus which prevents leakage of an electromagneticwave and stably operates while employing a simplified configuration.

To solve the above problem, the first aspect of the present inventionprovides a power line carrier communication apparatus including atransmission circuit which is connected to a power line and whichtransmits a signal to the power line; a reception circuit which isconnected to the power line and which receives the signal from the powerline; and an output suppression circuit which is connected to the powerline and which, by connecting a signal attenuating element between thetransmission circuit and a common only when the transmission circuittransmits the signal, suppresses an output of the signal transmittedfrom the transmission circuit.

According to the power line carrier communication apparatus, the outputsuppression circuit suppresses the signal transmitted from thetransmission circuit only when the signal is transmitted, so that it ispossible to weaken an intensity of the signal to be transmitted andprevent a negative influence on other electrical devices due to aleakage flux from a power line. Further, the signal received from thepower line is not attenuated by the output suppression circuit, so thatthe intensity of the received signal is not weakened.

A size of the signal attenuating element is preferably set according toa length of a power line which performs power line carrier communicationand an impedance of the power line, and, since the power line suppliespower, a configuration is preferably employed where the impedance is setlow and the amplitude of the signal transmitted from the transmissioncircuit is set to be low by the signal attenuating element and theoutput impedance from the transmission circuit can be decreased.

In addition, although the signal attenuating element is connected to acommon, in case of a vehicle, a housing of the vehicle is used as anearth common and this earth common is preferably used as a common(common potential) of power line carrier communication. In addition, itgoes without saying that, as a common, a minus power line or the likewhich can provide a common potential may be used.

The transmission circuit may be various amplifiers, and an element whichperforms switching by controlling a voltage at an operating point suchas a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) whichcan quickly perform switching is preferably used. In this case,switching elements are two switching elements connected in seriesbetween a plus power source and a minus power source of the transmissioncircuit, and, by controlling these switching elements to alternatelyturn on and off according to the transmission signal and connectingconnection points of both of the switching elements to the power line,it is possible to amplify and transmit the transmission signal. Further,the plus power source of the transmission circuit has a higher voltagethan the power source which supplies power to the power line.

In addition, it goes without saying that it is possible to provide thesame operation by using an IGFET (Insulated-Gate FET) or a MISFET(Metal-Insulator-Semiconductor FET) instead of the MOSFET.

When the output suppression circuit has: a voltage dividing resistancewhose one end is connected between an output resistance provided in anoutput unit of the transmission circuit and the power line; a switchingelement which connects another end of the voltage dividing resistance tothe common; and a switching control unit which places the switchingelement in an on state only when the transmission circuit transmits thesignal, it is possible to reliably attenuate the transmission signal byway of stable resistance voltage dividing.

The switching element is preferably formed by a FET such as a MOSFETwhich can perform on/off control at a high speed according to a voltage.When a common connected with the switching element is an earth common ofthe housing of the vehicle, there is a potential difference between thecommon and the power line and therefore a capacitor which cuts a directcurrent component is preferably connected in series to the outputresistance of the output suppression circuit.

When the reception circuit has: two capacitors which are connected inseries between both power sources of an amplifier which amplifies areceived signal; and a clipper circuit which connects connection pointsof these capacitors to the power line and limits the received signal ina predetermined range of a reference voltage between the capacitors, andthe amplifier compares the signal limited by the clipper circuit and thereference voltage and amplifies the signal, it is possible toarbitrarily set the reference voltage matching an operation of theamplifier, to the both power sources of the amplifier and amplify thereceived signal at around the reference voltage.

In addition, although at least two capacitors are provided to generatean intermediate reference voltage between the power sources, this by nomeans limits the number of capacitors which generate the referencevoltage.

The reference voltage is connected to the power line through the clippercircuit and is adequately adjusted to follow a voltage to be supplied tothe power line or a voltage of the received signal. Consequently, byamplifying the received signal at around the reference voltage, it ispossible to receive a received signal which is hardly influenced by avoltage fluctuation of the power line.

That is, although the impedance of the power line is low, and thereforewhen a signal is transmitted to this power line, a signal which has asquare wave upon transmission and which is received through the powerline becomes a distorted signal as if a waveform of the transmissionwave were subjected to a differential operation, it is possible totransform the distorted received wave into the original square wave byway of clipping performed by the clipper circuit and following of thereference voltage.

In addition, what is preferable is that the clipper circuit clips thereceived signal at a little potential difference to make the voltage ofthe power line easy to follow the reference voltage. Meanwhile, what ispreferable is that, when the clipper circuit performs clipping at agreat potential difference, it is possible to reduce an influence ofexternal noise. When, for example, the potential difference of thisclipping is 0.4 mV, the clipper circuit operates with a good balance andthe clipper circuit in this case can be formed with Schottky barrierdiodes which are mutually connected in the opposite direction.

When the amplifier is a differential amplifier which performs positivefeedback amplification, the output of the amplifier at around thereference voltage can be easily shaped such that the received signal hasa square wave in an output range of the amplifier.

As described above, the present invention can stably perform basebandcommunication through a power line using a switching element switched ata comparatively low speed and reduce manufacturing cost accordingly.Further, the operation is stable, so that the present invention canminimize an influence of external noise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a communication system which uses powerline carrier communication apparatuses according to a first embodimentof the present invention;

FIG. 2 is a view illustrating in detail a configuration of the powerline carrier communication apparatus illustrated in FIG. 1;

FIG. 3 is a view explaining an operation of the power line carriercommunication apparatus;

FIG. 4 is another view explaining the operation of the power linecarrier communication apparatus;

FIG. 5 is another view explaining the operation of the power linecarrier communication apparatus; and

FIG. 6 is another view explaining the operation of the power linecarrier communication apparatus.

DETAILED DESCRIPTION OF THE INVENTION

A power line carrier communication apparatus 1 according to a firstembodiment of the present invention will be described below using FIGS.1 to 4. As illustrated in FIG. 1, the power line carrier communicationapparatus 1 according to the present invention is used for acommunication system 2 of a vehicle.

The communication system 2 illustrated in FIG. 1 has: an electroniccontrol unit (ECU) 3 which performs communication with, for example,each electrical device provided at each door of the vehicle; powerwindow switches 4A, 4B . . . which are provided at the doors of thevehicle and operate windows to open and close; a window lock switch 5which is provided at a door on a driver's seat side and forbids anoperation of opening and closing the windows other than a window of thedriver's seat; motors 6A, 6B . . . which are driving sources of power toopen and close the windows; a contact point information collectingapparatus 7A which is connected to the electrical devices 4A, 5 and 6Aon the driver's seat side and inputs and outputs contact pointinformation; a contact point information collecting apparatus 7B whichis connected to the electrical devices 4B, . . . , 6B . . . provided atthe other doors and inputs and outputs contact point information; and apower line 9 which supplies power from a battery 8.

Further, the power line 9 not only transmits power but also functions asa signal line which connects the ECU 3 to the connection pointinformation collecting apparatuses 7A, 7B . . . and performs power linecarrier communication. In addition, in the following description, whenthe members 4A, 4B, . . . , 6A, 6B, . . . , 7A, 7B . . . do not need tobe distinguished, the members will be simply described using referencenumerals 4, 6 and 7.

The ECU 3 and the connection point information collecting apparatus 7Aand 7B have the power line carrier communication apparatuses 1 accordingto the present invention at connection portions with the power line 9.The power line carrier communication apparatus 1 has: a transmissioncircuit 10 which is connected to the power line 9 and which transmits asignal to the power line 9; a reception circuit 11 which is connected tothe power line 9 and which receives the signal from the power line 9;and an output suppression circuit 12 which is connected to the powerline 9 and which suppresses an output of the signal transmitted from thetransmission circuit 10.

The transmission circuit 10 has an amplification circuit 10A and anoutput resistance 10B, and the output suppression circuit 12 has avoltage dividing resistance 12A which is an example of a signalattenuating element whose one end is connected between the outputresistance 10B and the power line 9, a capacitor 12B which is connectedto the voltage dividing resistance 12A and blocks a direct currentcomponent, and a switching circuit 12 c which connects the other end ofthis capacitor 12B to a common (an earth common in case of a vehicle).

In addition, a CPU 3A in the ECU 3 performs computation processing ofmonitoring contact point information of the electrical devices 4A, 4B, .. . and 5 and outputting the contact point information for controllingthe motors 6A, 6B . . . , and the like and the contact point informationcollecting apparatuses 7A, 7B and . . . have input/output units 7P whichtransmit and receive the contact point information to and from the CPU3A, output the contact point information to the motors 6A, 6B . . . andreceive an input of the contact point information from the switches 4Aand 4B.

FIG. 2 is a view illustrating in detail a configuration of the powerline carrier communication apparatus 1. As illustrated in FIG. 2, thetransmission circuit 10, the reception circuit 11 and the outputsuppression circuit 12 adopt plus power sources Vcc of the CPU 3A or theinput/output units 7P as plus power sources which are formed accordingto signal levels of the CPU 3A or the input/output units 7P connected tothe transmission circuit 10, the reception circuit 11 and the outputsuppression circuit 12, and adopt a common earth common C as a minuspower source for the CPU 3A or the input/output units 7P.

The amplification circuit 10A of the transmission circuit 10 is formedwith MOS type FETs 20 and 21 of a N channel and a P channel, is formedby connecting a source of the FET 20 to the minus power source C, asource of the FET 21 to a plus power source Vcc and a drain of the FET20 to a drain of the FET 21 as indicated in FIG. 2, and receives aninput of A phase and B phase signals of opposite phases to betransmitted to gates of these FETs 20 and 21 as input unit signals, and,consequently, can generate a transmission signal which sets powervoltage levels of the power sources Vcc and C to a high level and a lowlevel to output the transmission signal to a power line connectionportion 9A to which the power line 9 is connected through the outputresistance 10B. In addition, a diode 22 prevents a backflow.

The reception circuit 11 has: an input resistance 23 which is connectedto the power line connection portion 9A; a capacitor 24 which cancelshigh frequency noise and has low capacity; two capacitors 25 and 26which are connected in series between the power sources Vcc and C; aclipper circuit 27 which connects the connection points of thesecapacitors 25 and 26 to the power line 9 through the input resistance23, and limits a received signal in a predetermined range of a referencevoltage Vth between the capacitors; an operation amplifier (which is anexample of a differential amplifier and is referred to as an OPamplifier below) 28 which compares the signal limited by the clippercircuit 27 and the reference voltage Vth and amplifies the signal; apositive feedback resistance 29 which provides a positive feedback ofthe output of this OP amplifier 28 to a non-inverting input terminal ofthe OP amplifier; and a capacitor 30 which stabilizes the output and haslow capacity.

In addition, backflow prevention diodes 23A and 23B are provided on asecondary side of the input resistance 23, and an output unit 11Aoutputs a signal generated as a square wave by the reception circuit 11.

The clipper circuit 27 has Schottky barrier diodes 27A and 27B which areconnected in parallel in opposite directions, and can clip an inputsignal by these diodes such that a potential difference between aninverting input terminal and the non-inverting input terminal of the OPamplifier is suppressed to about 0.4 V of forward drop voltages of theSchottky barrier diodes 27A and 27B.

Further, when the voltage of the power line 9 fluctuates due to a stateof a vehicle, and when the potential difference exceeds the forward dropvoltages of the Schottky barrier diodes 27A and 27B, an current flowsbetween the capacitors 25 and 26 through the clipper circuit 27, so thatit is possible to automatically adjust the reference voltage Vth betweenthe capacitors 25 and 26 according to a current state. By contrast withthis, in a range of the drop voltage of the clipper circuit 27, evenwhen noise is added to a voltage on the secondary side of the receptionresistance 23, an error of a received signal due to this noise is notproduced.

That is, by adequately adjusting constants of the members 23 to 30according to environment such as the length and the impedance of thepower line 9 used for signal communication, even baseband transmissioncan perform communication which is hardly influenced by noise.

Even though the waveform of a signal to be transmitted through the powerline 9 is a square wave upon transmission, the waveform is usuallysignificantly deformed upon reception and, above all, when a signal issuperimposed on the power line 9 of the low impedance, the waveform isdeformed as if the waveform were subjected to the differentialoperation. However, the clipper circuit 27 suppresses the referencevoltage Vth±forward drop voltage and the OP amplifier performs positivefeedback amplification, so that it is possible to effectively reproducethe original square wave even on the reception side.

The switching circuit 12C of the output suppression circuit 12 has: adiode 31 which is connected to an input unit 10C of the A phase signal;an inversion circuit 32 which is connected to the input unit 10D of theB phase signal; a switch control unit 35 which is formed with aresistance 34 connected to a connection point 33 of the diode and theinversion circuit; and a FET 36 (switching element) of a n channel whosegate is connected to the connection point 33. The switching circuit 12Cwhich is configured as described above performs switching such that theswitching circuit is placed in an on state only when a transmissionsignal is transmitted, and the source of the FET 36 is connected to anearth common C.

Consequently, a voltage dividing resistance 12A connected to a drain ofthe FET 36 is connected to the earth common C through the capacitor 12Bonly when a transmission signal is outputted. In addition, a capacitor12D is connected in parallel to the voltage dividing resistance 12A andthe capacitor 12B connected in series, and, by this means, the highfrequency component can flow to the earth common C without passingthrough the voltage dividing resistance 12A. In addition, a ratio ofsizes of the output resistance 10B and the voltage dividing resistance12B influences the degree of output suppression, and is adjustedaccording to the length or the magnitude of the impedance of the powerline 9 used to transmit and receive a signal.

FIGS. 3 to 6 are views illustrating examples where the operation of thepower line carrier communication apparatus 1 employing the aboveconfiguration is actually measured, and FIGS. 3 and 4 explain operationsof the transmission circuit 10 and the output suppression circuit 12 andFIGS. 5 and 6 explain the operation of the reception circuit 11.

A signal S1 illustrated in FIGS. 3 and 4 is superimposed on the powerline, and includes both of a transmission signal S1 s to be transmittedto the power line 9 through the power line connection portion 9A and areceived signal S1 r received from the power line 9. A switch signal S2indicates a voltage at the connection point 33 and this switch signal S2is an on/off signal of the switching element 36. A received signal S3 isreceived by the reception circuit 11, and is outputted to the outputunit 11A.

The switching circuit 12C enters an on state only when outputs of thediode 31 and the inversion circuit 32 are at a high level (during timest1 to t2, t3 to t4 and t5 to t6 illustrated in FIG. 4), and thereforecontinues to be on at all times while the input units 10C and 10Dreceive inputs of the A phase and B phase transmission signals and thetransmission signals are outputted. Consequently, the output of theamplification circuit 10A is earthed to the earth common C through theoutput resistance 10B, the voltage dividing resistance 12A and theswitching element 36, so that the output signal is attenuated bydividing the voltage by resistance values of the output resistance 10Band the voltage dividing resistance 12A and is transmitted to the powerline 9.

On the other hand, when the received signal S1 r is received, the switchsignal S1 becomes off, and therefore the voltage dividing resistance 12Ais not earthed to the earth common C and the received signal S1 rinputted through the power line connection portion 9A is not attenuatedby the voltage dividing resistance 12A. Switching between transmissionand reception of this signal is clearly distinguished when communicationaccording to a token passing method is performed, and a transmissiontiming of the power line carrier communication apparatus is known, sothat it is possible to reliably switch on and off of the switchingelement 36.

The operation is performed as described above, so that the intensity ofthe transmission signal S1 s supplied to the power line 9 issubstantially the same as the intensity of the received signal S1 rreceived from the power line 9. That is, even in environment in which aleakage flux is likely to be produced from the power line 9, it ispossible to easily suppress an output to such a degree that the leakageflux as an electromagnetic wave does not negatively influence externaldevices.

Further, it is not necessary to use a switching element which supports ahigh speed operation as in the case of using carrier waves (carrier) ofa high frequency, for every member which forms the power line carriercommunication apparatus 1, so that it is possible to reducemanufacturing cost accordingly.

Next, a received signal S4 illustrated in FIGS. 5 and 6 is on thesecondary side of the reception resistance 23, a signal S5 indicates avoltage fluctuation of the reference voltage with and a received signalS6 is a signal which is received and shaped into a square wave.

As illustrated in FIG. 5, the reference voltage which is determined bythe capacitors 25 and 26 (see FIG. 2) can fluctuate when the voltage tobe supplied to the power line 9 fluctuates to follow the change of thevoltage. That is, the reference voltage Vth is automatically adjustedaccording to a current power voltage supplied to the power line 9, andserves as an operating point of the OP amplifier 28. Further, thereceived signal S1 r received through the reception resistance 23 islimited in a range of about ±0.4 V of the reference voltage Vth similarto the signal S4.

Next, the output of the OP amplifier 28 rises or falls to the samedegree as that of the plus and minus power voltages Vcc and B dependingon the received signal. That is, the output of the reception circuit 11becomes a virtually square wave.

Although, as is obvious from FIG. 6, when the power line 9 of a lowimpedance is used for power superimposition of baseband transmission,the signal S1 s to be transmitted is distorted as if the signal issubjected to a differential operation, it is possible to shape theoutput waveform of the reception circuit 11 into the same square wave asthat upon transmission and perform communication with less error.

What is claimed is:
 1. A power line carrier communication apparatuscomprising: a transmission circuit which is connected to a power lineand which transmits a signal to the power line; a reception circuitwhich is connected to the power line and which receives the signal fromthe power line; and an output suppression circuit which is connected tothe power line and which, by connecting a signal attenuating elementbetween the transmission circuit and a common only when the transmissioncircuit transmits the signal, suppresses an output of the signaltransmitted from the transmission circuit.
 2. The power line carriercommunication apparatus according to claim 1, wherein the outputsuppression circuit includes: a voltage dividing resistance whose oneend is connected between an output resistance provided in an output unitof the transmission circuit and the power line; a switching elementwhich connects another end of the voltage dividing resistance to thecommon; and a switching control unit which places the switching elementin an on state only when the transmission circuit transmits the signal.3. The power line carrier communication apparatus according to claim 1,wherein the reception circuit includes: two capacitors which areconnected in series between both power sources of an amplifier whichamplifies a received signal; and a clipper circuit which connectsconnection points of these capacitors to the power line and limits thereceived signal in a predetermined range of a reference voltage betweenthe capacitors, and the amplifier compares the signal limited by theclipper circuit and the reference voltage and amplifies the signal. 4.The power line carrier communication apparatus according to claim 3,wherein the amplifier is a differential amplifier which performspositive feedback amplification.